We constructed a vaccinia virus recombinant which expressed bovine rotavirus glycoprotein VP7 (the major neutralization protein) by inserting a cDNA copy of the 9th gene from NCDV into the TK gene of vaccinia virus. This recombinant virus expressed a polypeptide of approximately 35,000 dalton which migrated closely with VP7 of NCDV. We vaccinated two rabbits with this recombinant virus intradermally and observed their response by various serological methods. Immunofluorescent and plaque reduction neutralization tests showed a significant increase in titer following vaccination although relatively high levels of pre-existing antibody to rotavirus made proper interpretation difficult. This preliminary experiment demonstrated the necessity of using animals lacking rotaviruses antibody in further animal experiments to determine the antigenicity of this recombinant. We screened sera from cotton rats, mice, hamsters, guinea pigs and rabbits by neutralization assay. Although many of the animals had rotavirus antibody, it appeared that if a sufficient number of mice, hamsters, or guinea pigs were used, a small proportion should have little, if any, antibody. Thus, mice and hamsters have been inoculated with the recombinant vaccine virus to study their serological response to the NCDV VP7 component of the vaccinia-rotavirus VP7 recombinant.